ARCHIVED REPORTS XR0009296 - Laserfiche WebLink

Home Browse Search

"'"bglca!rechlaa Jac Page 8 Groundwater Monitoring Report Project No 723 2 April 24,2006 ' ❑ The shallow aquifer ui aq gradient for the event was to the northeast that is consistent with the ' previous event ❑ The vertical gradient is predominately downward, which has contributed to the depth that this contaminant plume has migrated ' ❑ The concentrations of BTEX and TPH-G continue to fluctuate to individual monitoring wells from one sampling event to the next However, there is a general trend of concentrations tracking the groundwater elevations ' ❑ The main mass of contaminants appears to have migrated to the depth of the intermediate well screen interval (43 to 70 ft bgs) ❑ On site deepest well MW-101 intermittently contains BTEX contaminants and it ' contained low levels TPH-G for the event The TPH-G concentrations in MW-101 have exhibited a slight increasing trend since March 2004 ❑ Deep well MW-201 occasionally contains trace BTEX but was non-detect for the event ' The intermittent contamination is probably a drilling artifact created by the use of mud rotary drilling The contaminant concentration decline since the first monitoring event in December 2001 supports the conclusion that the initial high concentrations were from a ' drilling artifact ❑ Figure 10 illustrates TPH-G and Benzene concentrations versus elevation in well MW-3, which lies near the core of the plume There appears to be a fairly direct relationship between the water table and the TPH-G concentrations Benzene concentrations have stabilized in the well ❑ Figure 1 i illustrates TPH-G and Benzene concentrations versus elevation in well MW-4, ' which lies up gradient of the core of the plume The contaminant concentrations exhibit a decreasing trend in this well ❑ Figure 12 illustrates TPH-G and Benzene concentrations versus elevation in deep well ' MW-101, which lies near the core of the plume The TPH-G and benzene concentrations displayed a decreasing trend until early 2004 and an increasing trend for the past two ' years The steep decline in the initial concentrations suggests that the contaminants detected in the well were initially a drilling artifact The recent events suggest that the well intercepts the bottom of the plume ' ❑ Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements (Table 7) show that most of the wells monitored are screened in areas of the groundwater plume that are affected by the biodegradation reactions occurring within the plume The low to ' highly negative ORP values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants The low DO values of the wells also reflected this condition 3.0 CONCLUSIONS & RECOMMENDATIONS ' Conclusions • I Groundwater flow trends northeast to east The southerly flow direction recorded on ' December 4, 2000, appears to be anomalous The deepest Set of CMTs'- wells displayed